Problem with retrieving order via REST API

I’m trying to retrieve an order using this code:

<?php
 require '/home/username/vendor/autoload.php';

 use Automattic\WooCommerce\Client;
 use Automattic\WooCommerce\HttpClient\HttpClientException;

 $wc = new Client(
     'https://www.website.com/wp',
     'ck_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx',
     'cs_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx',
     [
         'wp_api' => true,
         'version' => 'wc/v1',
         'query_string_auth' => true,
     ]
 );
 try {
     $results = $wc->get("orders/418");
     print_r($results);
 } catch (HttpClientException $e) {
     echo $e->getMessage() . "\n\n";
     echo print_r($e->getRequest(), true) . "\n\n";
     echo print_r($e->getResponse()) . "\n\n";
 }
 ?>

This is the output:

Syntax error

Automattic\WooCommerce\HttpClient\Request Object
(
    [url:Automattic\WooCommerce\HttpClient\Request:private] => https://www.website.com/wp/wp-json/wc/v1/orders/418?consumer_key=ck_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx&consumer_secret=cs_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
    [method:Automattic\WooCommerce\HttpClient\Request:private] => GET
    [parameters:Automattic\WooCommerce\HttpClient\Request:private] => Array
        (
            [consumer_key] => ck_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
            [consumer_secret] => cs_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
        )

    [headers:Automattic\WooCommerce\HttpClient\Request:private] => Array
        (
            [Accept] => application/json
            [Content-Type] => application/json
            [User-Agent] => WooCommerce API Client-PHP/1.1.1
        )

    [body:Automattic\WooCommerce\HttpClient\Request:private] =>
)

Automattic\WooCommerce\HttpClient\Response Object
(
    [code:Automattic\WooCommerce\HttpClient\Response:private] => 200
    [headers:Automattic\WooCommerce\HttpClient\Response:private] => Array
        (
            [Server] => nginx

            [Date] => Fri, 08 Jul 2016 09:44:28 GMT

            [Content-Type] => application/json; charset=UTF-8

            [Transfer-Encoding] => chunked

            [Connection] => keep-alive

            [X-Content-Type-Options] => nosniff

            [Access-Control-Expose-Headers] => X-WP-Total, X-WP-TotalPages

            [Access-Control-Allow-Headers] => Authorization

            [Expires] => Wed, 11 Jan 1984 05:00:00 GMT

            [Cache-Control] => no-cache, must-revalidate, max-age=0

            [Pragma] => no-cache

            [Last-Modified] => Thu, 01 Jan 1970 00:00:00 GMT

            [Host-Header] => 192fc2e7e50945beb8231a492d6a8024

            [X-Proxy-Cache] => MISS

        )

    [body:Automattic\WooCommerce\HttpClient\Response:private] => <br />
<b>Notice</b>:  Undefined variable: post in <b>/home/username/public_html/wp/wp-content/plugins/woocommerce/includes/abstracts/abstract-wc-rest-posts-controller.php</b> on line <b>141</b><br />
<br />
<b>Notice</b>:  Trying to get property of non-object in <b>/home/username/public_html/wp/wp-content/plugins/woocommerce/includes/abstracts/abstract-wc-rest-posts-controller.php</b> on line <b>141</b><br />
<br />
<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /home/username/public_html/wp/wp-content/plugins/woocommerce/includes/abstracts/abstract-wc-rest-posts-controller.php:141) in <b>/home/username/public_html/wp/wp-includes/rest-api/class-wp-rest-server.php</b> on line <b>1196</b><br />
{"code":"woocommerce_rest_invalid_shop_order_id","message":"Invalid id.","data":{"status":404}}
)
1

The order id is definetely valid, I can see it when I list all orders with $wc->get(“orders”). I’ve tried retrieving customers and product in an analogous way and it worked fine.
Am I doing something wrong?

https://wordpress.org/plugins/woocommerce/